According to the video, the spacecraft uses reaction wheels for pointing, and there is no chemical RCS (ie no thrusters). So, how does a spacecraft without propulsive thrusters de-saturate the reaction wheels?

Almost certainly magnetic torquers, like Hubble. (These are really common for cubesats and probably microsats as well.)

According to the video, the spacecraft uses reaction wheels for pointing, and there is no chemical RCS (ie no thrusters). So, how does a spacecraft without propulsive thrusters de-saturate the reaction wheels?

Almost certainly magnetic torquers, like Hubble. (These are really common for cubesats and probably microsats as well.)

Do magnetic torquers work beyond LEO?

Not in GSO, if that's what you mean, since that's beyond the magnetosphere. This is partly why the 200 and 300 series are set to use propulsion (most certainly not the only reason).

Logged

Chris Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

They seem like smart people who are willing to put lots of capital into their project without short-term return...The PR business plan seems to make sense in two short-term scenarios, PGMs ...and water/LH2/LOX

Actually, I think the short-term scenario has more to do with their belief in exponential technology improvements (based on Diamandis' book). I think that in the short term, they feel confident about likely breakthroughs in optical interferometry and laser communication at interplanetary distances. Proving these out with satellites that they can manufacture for a few million dollars each, and launch as secondary payloads for a few million dollars each, would instantly allow them to dominate a multi-billion dollar industry, and expand markets. Creating a catalog of NEO's would start as a philanthropic venture, watching for rogue Earth smashers, and through that process they would be collecting valuable data on optical properties of these things from a difference. They may find (and are likely to find imo) highly concentrated bodies. But arkyd 200 phase will probably be at least 5 years out (I hope I'm wrong).

I'm not sure what excites me more about the potential of Planetary Resources:Having a catalogue of potentially civilization saving information (orbits of NEO's)Discovering zillions of exoplanets through optical interferometryThe new data we can collect about our solar system, including through visual observations.A map of noteable Kuiper and Oort objects along with high-res photos of many of them.The improved resolution of various interstellar phenomenonHaving very regular high-res updates (and historical database) to google earth (or perhaps it will be called PR-Earth)The potential for abundant volatiles and metals that could be processed in space and used for in-space habitation and transportation by all comersThe impact it will have on STEM outreach

I'm not sure what excites me more about the potential of Planetary Resources:Having a catalogue of potentially civilization saving information (orbits of NEO's)Discovering zillions of exoplanets through optical interferometryThe new data we can collect about our solar system, including through visual observations.A map of noteable Kuiper and Oort objects along with high-res photos of many of them.The improved resolution of various interstellar phenomenonHaving very regular high-res updates (and historical database) to google earth (or perhaps it will be called PR-Earth)The potential for abundant volatiles and metals that could be processed in space and used for in-space habitation and transportation by all comersThe impact it will have on STEM outreach

My understanding about telescopes is that they need to be focused on a specific distance - so a constellation aimed at finding NEOs are not going to produce a bunch of data on Kuiper Belt objects.

a constellation aimed at finding NEOs are not going to produce a bunch of data on Kuiper Belt objects.

I am assuming they won't be all aimed at NEO's all the time. "swarms".

If discovering valuable NEOs = money, then every second not looking for NEOs has significant opportunity cost.

More to the point, the telescopes used by PR will be optimized for close object; space isn't like Star Trek, where every system can be quickly reconfigured for other purposes, like using the deflector dish as a weapon; in this case, if the telescopes are not optimized for business purposes, there will be a significant cost.

Where are all these wild expectations about using the telescopes for interferometry coming from? Has the PR even hinted at that?

Yes. From their website:

They seem to have taken it down now, but there was mention of improvements over current stabilization technology by more than 2 orders of magnitude. This implies optical interferometry (I believe).

The watered-down quote now says:

"Central to its configuration and functionality is a precision imaging system. With arc-second resolution, the Leo spacecraft camera will provide detailed celestial and Earth observations where you want them, and when you want them. Leo is capable of surveying for near-Earth asteroids during one orbit, then be retasked for rain forest observation on the next. The possibilities for utility and engagement are only limited by the imagination of the user."

More to the point, the telescopes used by PR will be optimized for close object; space isn't like Star Trek, where every system can be quickly reconfigured for other purposes, like using the deflector dish as a weapon; in this case, if the telescopes are not optimized for business purposes, there will be a significant cost.

I'm not sure what excites me more about the potential of Planetary Resources:Having a catalogue of potentially civilization saving information (orbits of NEO's)Discovering zillions of exoplanets through optical interferometryThe new data we can collect about our solar system, including through visual observations.A map of noteable Kuiper and Oort objects along with high-res photos of many of them.The improved resolution of various interstellar phenomenonHaving very regular high-res updates (and historical database) to google earth (or perhaps it will be called PR-Earth)The potential for abundant volatiles and metals that could be processed in space and used for in-space habitation and transportation by all comersThe impact it will have on STEM outreach

My understanding about telescopes is that they need to be focused on a specific distance - so a constellation aimed at finding NEOs are not going to produce a bunch of data on Kuiper Belt objects.

I'm not sure what excites me more about the potential of Planetary Resources:Having a catalogue of potentially civilization saving information (orbits of NEO's)Discovering zillions of exoplanets through optical interferometryThe new data we can collect about our solar system, including through visual observations.A map of noteable Kuiper and Oort objects along with high-res photos of many of them.The improved resolution of various interstellar phenomenonHaving very regular high-res updates (and historical database) to google earth (or perhaps it will be called PR-Earth)The potential for abundant volatiles and metals that could be processed in space and used for in-space habitation and transportation by all comersThe impact it will have on STEM outreach

My understanding about telescopes is that they need to be focused on a specific distance - so a constellation aimed at finding NEOs are not going to produce a bunch of data on Kuiper Belt objects.

Wouldn't the telescope simply be focused to infinity?

cheers, Martin

I was waiting to see who would notice that - at about 1000 focal lengths, the object is at optical infinity, once the optic is set to infinity focus all objects observed beyond that distance will be "in focus". Any telescope built in the foreseeable future orbiting near earth will be set to infinity when looking out at astronomical objects including asteroids (looking down at the earth or in near space might need to be focused).

I'm not sure what excites me more about the potential of Planetary Resources:Having a catalogue of potentially civilization saving information (orbits of NEO's)Discovering zillions of exoplanets through optical interferometryThe new data we can collect about our solar system, including through visual observations.A map of noteable Kuiper and Oort objects along with high-res photos of many of them.The improved resolution of various interstellar phenomenonHaving very regular high-res updates (and historical database) to google earth (or perhaps it will be called PR-Earth)The potential for abundant volatiles and metals that could be processed in space and used for in-space habitation and transportation by all comersThe impact it will have on STEM outreach

My understanding about telescopes is that they need to be focused on a specific distance - so a constellation aimed at finding NEOs are not going to produce a bunch of data on Kuiper Belt objects.

Wouldn't the telescope simply be focused to infinity?

cheers, Martin

I was waiting to see who would notice that - at about 1000 focal lengths, the object is at optical infinity, once the optic is set to infinity focus all objects observed beyond that distance will be "in focus". Any telescope built in the foreseeable future orbiting near earth will be set to infinity when looking out at astronomical objects including asteroids (looking down at the earth or in near space might need to be focused).

If that were the case, wouldn't Hubble already have even better coverage of the near Earth region?

I'm not sure what excites me more about the potential of Planetary Resources:Having a catalogue of potentially civilization saving information (orbits of NEO's)Discovering zillions of exoplanets through optical interferometryThe new data we can collect about our solar system, including through visual observations.A map of noteable Kuiper and Oort objects along with high-res photos of many of them.The improved resolution of various interstellar phenomenonHaving very regular high-res updates (and historical database) to google earth (or perhaps it will be called PR-Earth)The potential for abundant volatiles and metals that could be processed in space and used for in-space habitation and transportation by all comersThe impact it will have on STEM outreach

My understanding about telescopes is that they need to be focused on a specific distance - so a constellation aimed at finding NEOs are not going to produce a bunch of data on Kuiper Belt objects.

Wouldn't the telescope simply be focused to infinity?

cheers, Martin

I was waiting to see who would notice that - at about 1000 focal lengths, the object is at optical infinity, once the optic is set to infinity focus all objects observed beyond that distance will be "in focus". Any telescope built in the foreseeable future orbiting near earth will be set to infinity when looking out at astronomical objects including asteroids (looking down at the earth or in near space might need to be focused).

If that were the case, wouldn't Hubble already have even better coverage of the near Earth region?

As far as if Hubble is better adapted for NEO searches... That's a different question. You must first realize that NEO searches take a long time to get a lot of hits and that Hubble 'scope time is VERY precious. Also, resolution isn't what you're primarily concerned with when looking for NEOs, so Hubble isn't necessarily THAT much better than a smaller aperture scope (although the raw collecting area helps for some things, obviously).

Logged

Chris Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

My point here is: if telescopes focused on infinity can resolve near Earth objects as well as far away stars, given that Hubble has been pointing out for some 20 years, it should have an enormous number of images of NEOs as a by-product of its star searches.

NASA has money to purchase NEO data. So PR could sell its data to NASA to almost get the cost of operating and possibly developing its satelllites paid for.

Especially since PR would be doing the NEO data collection with or without NASA money.

I hope you understand that when NASA puts money in its budget for a line item, the money is allocated very carefully ahead of time. Its very rare that NASA would redirect funding for a cost center to another cost center.

In this specific case, the money is going to be used for part of the cost of operating Goldstone and other facilities.

Oh, yes, this is FY 2012 money, and since PR is not going to be finding any NEOs in FY 2012, its all moot.

My point here is: if telescopes focused on infinity can resolve near Earth objects as well as far away stars, given that Hubble has been pointing out for some 20 years, it should have an enormous number of images of NEOs as a by-product of its star searches.

Nope, Hubble is not a survey scope. It spends a lot of time looking at deep field objects and doing VERY long exposures, not lots of short exposures like a survey telescope does. And yes, survey telescopes (like WISE, for instance) do catch a lot of NEOs.

Also, some parts of the sky are more likely to have NEOs than others. To first order, the Ecliptic Plane is where you want to look for NEOs. And Hubble has reasons to avoid the ecliptic plane, like zodiacal light (and gegenschein, its antisolar counterpart), which can ruin nice exposures of deep field objects.

Logged

Chris Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

When I'm not sweeping the floors, I sometimes build/design optical systems - just for the fun of it.Hubble was designed for long duration imaging of deep space objects, exposures of several hours or more are routinely done, near earth objects move in and out of the field of view in small portions of the exposure period and are not imaged as such.Hubble is a near-diffraction limited optical system, resolution is a function of aperture, it can image near earth objects well - like the moons of our solar system planets like those of Jupiter. If the telescope can slew fast enough and long enough it could capture images of asteroids etc., I don't know if it can. Further, Hubble does not resolve stars beyond a disk of light - no spatial detail only spectral - note that the stars in the images don't have detail.The small scopes that are being proposed will most likely get reasonable spectral data on the asteroids and little spatial. Synthetic aperture imaging with multiple optics will require sub-nanosecond clocks to combine the images - do they have those?